The present invention relates to an antenna array and, in particular, to an antenna array for wireless articles.
Increasingly, technological means are desired for detecting the presence of people and articles, for identifying people and articles, and for tracking people and articles. Applications of such technology run the gamut, from theft detection devices used in food markets, department stores and other retail establishments, to inventory of products and warehouse stocks, to the control, routing and tracking of baggage at airports, train stations and other travel facilities, and for providing selective access and/or security for personnel and facilities such as hotels, schools, businesses, government facilities and the like, to name but a few.
Conventional prior art systems typically employ a detection portal such as that illustrated in FIG. 1. Portal 2 includes two parallel planar panels 4 each containing a loop antenna coupled to a detector. Panels 4 are supported by base 6. Prior art portal 2 typically is utilized with xe2x80x9ctagsxe2x80x9d that may simply be a small sheet of a metal foil or a simple non-linear electronic device such as a diode coupled to a loop antenna. The presence of such tag in the region between the parallel panels 4 results in a distortion of the radio frequency (RF) signal transmitted by the antennas in panels 4 which is detected and utilized to set off an alarm, such as a buzzer, bell or other audible alarm and/or a light, flashing light or other visible alarm. Thus the system is simply a proximity detector for a tag in the proximity of panels 4.
More sophisticated detection systems might desire to not only detect the presence of a tagged article or person, but also to identify the article or person by identifying the tag. Such systems typically utilize a tag that includes an electronic device coupled to the loop antenna thereof, typically to respond to receipt of RF signals transmitted by the antenna of panels 4 by transmitting an identifying number or code, whereby apparatus to which panels 4 are connected identify the tag.
Conventional antenna arrays utilized in prior art portals typically are not capable of reading 100% of the tags passing in their proximity irrespective of the orientation of the RF tag, i.e. coupling to the antenna of the tag is inadequate at certain tag orientations. While 95% or 98% detection and accuracy may be satisfactory for many applications, it is not satisfactory for more demanding applications such as tracking passenger baggage for air travel, tracking factory and/or warehouse inventory, or identifying persons for security and/or access control.
Accordingly, it would be desirable to have an antenna array that is capable of detecting the presence of a wireless article such as an RF tag within its detection region with 100% accuracy or very close to 100% accuracy. It would also be advantageous if such antenna array was capable of operating with wireless articles that include an electronic device (also referred to as an integrated circuit or xe2x80x9cICxe2x80x9d or as a chip) including a memory so that information could be written into the memory of the wireless article as well as read from the memory and transmitted by the wireless article.
To this end, the antenna array of the present invention comprises at least two antenna loops disposed at an angle with respect to each other to define a detection region in which the two antenna loops transmit and/or receive electromagnetic signals having electromagnetic components in each of three mutually orthogonal directions and through which an object may pass. A processor processes at least received signals, and means couples the at least two antenna loops and the processor for coupling at least the received signals therebetween.